Passive Localization of Multiple Sources Using Widely-Spaced Arrays With Application to Marine Mammals

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1 Passive Localization of Multiple Sources Using Widely-Spaced Arrays With Application to Marine Mammals L. Neil Frazer School of Ocean and Earth Science and Technology University of Hawaii at Manoa 1680 East West Road Honolulu, HI, , USA phone: (808) fax: (808) Eva-Marie Nosal School of Ocean and Earth Science and Technology University of Hawaii at Manoa 1680 East West Road Honolulu, HI, , USA phone: (808) fax: (808) Award Number: N (OA Graduate Traineeship for E.-M. Nosal) LONG-TERM GOALS The long-term goal of our research is to develop systems that use a widely spaced hydrophone array to localize and track multiple unknown sources in shallow-water environments over long distances. OBJECTIVES The objectives of this project are: (i) Development of new theoretical frameworks for localization; (ii) Testing and fine-tuning of the theory and its implementation through simulations; and (iii) Application to whale data collected on widely spaced hydrophone arrays, including Navy arrays such as PMRF and AUTEC. APPROACH In all of our work, acoustic propagation models [1] are used as necessary.

2 Report Documentation Page Form Approved OMB No Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 30 SEP REPORT TYPE 3. DATES COVERED to TITLE AND SUBTITLE Passive Localization of Multiple Sources Using Widely-Spaced Arrays With Application to Marine Mammals 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) University of Hawaii at Manoa,School of Ocean and Earth Science and Technology,1680 East West Road,Honolulu,HI, PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT 11. SPONSOR/MONITOR S REPORT NUMBER(S) 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Same as Report (SAR) 18. NUMBER OF PAGES 8 19a. NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

3 Figure 1. Spectrograms (256 point FFT Hanning windows with 50% overlap) of typical sperm whale (top) and humpback whale (bottom) calls. Currently, two whale species are being considered for localization: humpback whales and sperm whales. Due to differences in their calls, each species requires a different approach to localization. Figure 1 shows spectrograms of sperm whale and humpback whale calls. Sperm whales emit so-called regular clicks which are broadband (100 Hz 20 khz) short in duration and predictable (Figure 1). These characteristics make sperm whales ideal candidates for time difference of arrival (TOAD) methods [2] (also known as hyperbolic fixing methods). TOAD methods use waveform or spectrogram correlation to estimate the difference in time of direct arrivals at hydrophone pairs. To provide an alternate approach that does not rely on TOADs, we developed a method that uses the difference in arrival times between direct and reflected arrivals (DRTDs) on individual hydrophones [3]. Since DRTD is a function of source-receiver separation for a fixed receiver and source at a single candidate depth, the DRTDs define circles around each hydrophone. These circles indicate most probable source positions (see Figure 2). The candidate depth and point at which receiver circles intersect most closely determines the estimated source position. The DRTD method can be used in combination with TOAD methods to provide more precise source location estimates.

4 Figure 2. Likelihood surfaces created using our DRTD method for three candidate source depths (from left to right: 400 m, 670 m, and 890 m). Receiver positions are shown as white triangles. The best estimated source position is (10010 m, m, 670 m). The humpback whale localization problem presents a considerably more challenging problem. Humpbacks are more difficult to localize because their calls (Figure 1) are highly varied, unpredictable, and of long duration (with individual calls of up to several seconds long) [4]. Humpback vocalizations are typically between 30 Hz and 9 khz. In addition, they usually vocalize in shallow water, so multiple propagation paths must be considered. These characteristics may render hyperbolic fixing methods (and our DRTD method) insufficient, particularly in the case of multiple whales. Conventional matched-field techniques may also be insufficient because they are limited to low frequencies and/or rely on line arrays [5,6]. To deal with the unknown nature of the sources, we developed the pair-wise waveform (PWW) processor [7]. Our pair-wise spectrogram (PWS) processor [7] extends the PWW processor by using spectrograms instead of waveforms. Spectrograms allow us to use high frequencies, which are sensitive to environmental mismatch and noise. The key individuals participating in this effort are L. Neil Frazer at the University of Hawaii and his Ph.D. student Eva-Marie Nosal. Both participants cooperate on all aspects of the work. WORK COMPLETED We developed and implemented the DRTD method. It was successfully applied to a dataset from the AUTEC range in the Bahamas. The work was reported in a paper in Applied Acoustics [3]. We developed and implemented the PWW and PWS processors. Due to high computational demand, our implementations were parallelized for use on supercomputers. Simulations were run for numerous environments and source/receiver configurations. The theory and initial simulations have been published in an OES Newsletter [7]. RESULTS For sperm whales our DRTD method has a distinct advantage over TOAD methods in that it is not sensitive to receiver timing offsets. This advantage was emphasized during the 2 nd International

5 Workshop on Detection and Localization of Marine Mammals, during which groups using TOAD methods could not localize the sperm whale source because of a 2.34 s receiver timing offset [8]. The DRTD method yielded an accurate whale track, which was similar to the track found by other groups after the timing offset had been discovered [8]. Figure 3 shows a 3D display of the resulting track. Figure 3. Three dimensional track of a sperm whale localized using the DRTD method and 5 bottom-mounted hydrophones in the AUTEC range. The track represents 25 minutes of data. Projections onto the three planes are shown with dotted lines. For humpback whales our simulations indicate [7] that our PWS processor is more robust with respect to environmental mismatch and noise than the Bartlett (linear matched-field) processor and the PWW processor. This is as expected, since spectrograms are less sensitive to changes in the environment than waveforms. Comparisons of the Bartlett, PWW, and PWS processors are shown in Figures 4 and 5.

6 Figure 4. Ambiguity surfaces (probabilistic indicators of source location) created using the Bartlett (top), PWW (middle), and PWS (bottom) processors. Data was simulated for a single source, three receivers, signal-to-noise ratio of 5 db. Environmental mismatch was simulated by using an incorrect bottom depth in the inversion (204 m instead of the correct depth of 200 m). Only the PWS processor correctly localizes the source.

7 Figure 5. Ambiguity surfaces created using the Bartlett (top), PWW (middle), and PWS (bottom) processors. Data was simulated for two sources, four receivers, and signal-tonoise ratio of 0 db. Environmental mismatch was simulated by using an incorrect bottom depth in the inversion (204 m instead of the correct depth of 200 m). Only the PWS processor correctly localizes both sources. IMPACT/APPLICATIONS The DRTD, PWW, and PWS processors are useful for monitoring, studying, and mitigating human impact on marine mammals. They may be also be used to monitor the ocean environment for other undersea and sea-surface sound sources.

8 RELATED PROJECTS None. REFERENCES [1] M.B. Porter, Acoustics Toolbox, [2] B. Møhl, M. Wahlberg, P.T. Madsen, L.A. Miller, A.M. Surlykke, Sperm whale clicks: directionality and source level revisited, J. Acoust. Soc. Am. 107(1), , [3] Nosal, E.-M., and Frazer, L. N., Delays between direct and reflected arrivals used to track a single sperm whale, Applied Acoustics, 87 (11-12), , Nov.-Dec [4] R. S. Payne and S. McVay, Songs of humpback whales, Science, 173, , [5] B. Baggeroer, W. A. Kuperman, and P. N. Mikhalevsky, An overview of matched field methods in ocean acoustics, IEEE J. Ocean. Eng., 18, , [6] A. Tolstoy, Matched field processing. Singapore: World Scientific, [7] Nosal, E.-M., and Frazer, L.N., Pair-wise processing of spectrograms for localization of multiple broadband CW sources, Proceeding of the IEEE Oceans 05 Europe meeting, Brest, France, June Special publication in the Newsletter of the IEEE OES, Winter [8] O. Adam, J.-F. Motsch, F. Desharnais, N. DiMarzio, D. Gillespie, and R. C. Gisiner, Overview of the 2005 workshop on detection of localization of marine mammals using passive acoustics, Applied Acoustics 87 (11-12), , PUBLICATIONS Nosal, E.-M., and Frazer, L. N., Modified pair-wise spectrogram processing for localization of unknown broadband sources, IEEE Journal of Oceanic Engineering [submitted, refereed]. Nosal, E.-M., and Frazer, L. N., Delays between direct and reflected arrivals used to track a single sperm whale, Applied Acoustics, 87 (11-12), , (Nov.-Dec. 2006) [published, referred] Nosal, E.-M., and Frazer, L.N., Pair-wise processing of spectrograms for localization of multiple broadband CW sources, Proceeding of the IEEE Oceans 05 Europe meeting, Brest, France, June Special publication in the Newsletter of the IEEE OES, Winter 2006 [published].

9 HONORS/AWARDS/PRIZES First Prize to E.-M. Nosal (University of Hawaii) IEEE OES Student Poster Program Oceans 05 Europe, Brest, France, June 20-23, Sponsored by Thales Underwater Systems. Student Engagement Award to E.-M. Nosal Maui High Performance Computing Center ( ).